We have said that some ILP approaches struggle to learn large programs.
However, what constitutes a large program is unclear.
Most authors measure the size of a logic program as either the number of literals [1]} or rules [2]} in it.
However, these two metrics for are too simple.
For instance, many approaches can easily learn programs with lots of clauses by simply memorising the examples.
Likewise, approaches based on inverse entailment [3]} can easily learn programs with lots of literals by simply returning the bottom clause.
In this paper we do not formally define what constitutes a large program.
By large, we informally mean programs with reasonably large numbers of rules, variables, and literals.
